However, the judge has approved the Labour Party's decision to appeal the court's decision, after five new members of the party won a High Court battle over their legal right to vote yesterday morning.

The ruling means the Labour leader could win with a larger mandate than previously expected.

The five accused the party's National Executive Committee (NEC) of unlawfully "freezing" them and many others out of the high-profile contest between Jeremy Corbyn and Owen Smith even though they had "paid their dues".

The news will come as a blow to the Labour leadership contender Owen Smith MP.

A Labour Party sportsperson said: "It is right that the Labour Party seeks to defend vigorously decisions of the National Executive Committee in this matter, and we will now study this judgement carefully."

Peter Oldham QC, appearing for the party, argued that the NEC had "specific power" to impose a freeze as part of its role in issuing an election timetable.

The NEC decided that full members would not be able to vote if they had not had at least six months' continuous membership up to July 12 - the "freeze date".

Stephen Cragg QC, appearing for the five, asked Mr Justice Hickinbottom, sitting in London, to declare that party rules had been misapplied and the five are entitled to vote in the September 24 poll.

In court, Mr Cragg told the judge that anyone looking on the party website, or reading its rule book, would have concluded that, having joined the party, there was nothing to stop the five from voting.

The judge, Mr Justice Hickinbottom, ruled that refusing the five the vote "would be unlawful as in breach of contract".

He said: "This case was always based primarily on the Labour party's constitution as set out in the rule book."

Edward Leir, one of the five members, said the court's ruling was a "victory for equality and inclusion".